OSAKA, Japan -- Charges of faulty maintenance were leveled against the operators of an amusement park in Japan after a cracked axle was found on a roller coaster train.

Authorities inspected a second train at Osaka's Expoland amusement park one month after the derailment of another park roller coaster killed a passenger, The Daily Yomiuri reported Monday.

An expert on material mechanics from Kobe University, Professor Toshimichi Fukuoka, said in his opinion the park operators had neglected proper maintenance.

"Axles bear loads from various directions like an Achilles tendon," he said. "As an abnormality also was found in the other train, I'd say the park operator neglected to sufficiently maintain them."

Each axle links a unit of five large and small wheels to the roller coaster car. If a crack develops and expands, the unit linked by the axle could drop off as it did in the fatal accident in May, the report said.

Park employees told police that only some of the axles on the trains were inspected, the Daily Yomiuri said.